To improve a yield of a material from which core sheets are stamped, a laminated rotor core is produced by stamping segment core sheets (also referred to as separate core sheets) in the form of divided core sheets, laminating the segment core sheets to form separate laminated cores, and subsequently assembling the separate laminated cores. Another method for producing a laminated rotor core with improved material yield involves stamping a band in predetermined shape consisting of connected segment core sheets, and spirally winding the band-shaped sheet.
When the laminated rotor core is produced by winding the band-shaped core sheet, the band-shaped core sheet in a straight form is stamped from a metal sheet, i.e., a material, thereby improving the material yield. In accordance with this method, however, the segment core sheets having a desired shape are stamped to be connected with each other thereby to form the band-shaped core sheet, and subsequently, one strip of the band-shaped core sheet is wound and laminated sequentially until the desired lamination thickness is achieved. Thus, the method is low in productivity.
In order to solve the above problem, Japanese Unexamined Patent Application Publication No. 11-299136, for example, proposes a method for producing a laminated core (laminated stator core) by superposing and integrating band-shaped core sheets, and subsequently winding the integrated sheets. FIG. 5 shows how the core is formed according to the method. Band-shaped core sheets 72, 73 are prepared in which pole sections 71 are formed at the inner sides of yoke pieces 70 at predetermined intervals. The band-shaped core sheets 72, 73 are piled and integrated with each other. Then, the core sheets 72, 73 are spirally wound and laminated around the periphery of a mandrel (inner diameter guide cylinder) 74 with the pole sections 71 of the sheets 72, 73 aligned with one another. According to the art disclosed in the publication, the integration of the piled sheets increases the thickness of the band-shaped core sheets, thereby improving productivity of the lamination. The reference numeral 75 designates an outer diameter guide cylinder.
According to the art disclosed in the publication, however, the integration of the superposed band-shaped core sheets 72, 73 requires, e.g., welding, which makes the manufacturing operation complicated. Additionally, the superposed and integrated band-shaped core sheets are increased in stiffness. Therefore, when a laminated core having a small diameter is produced according to the method, winding of the sheets is difficult and the formed shape is deteriorated, which may cause a problem, e.g., that the pole sections are not aligned in the laminating direction.
In view of the above, Japanese Unexamined Patent Application Publication No. 1-264548 proposes a method for producing a laminated core (laminated stator core) by spirally winding a plurality of band-shaped core sheets each having arc-shaped segment core sheets connected by connecting portions while displacing the positions of the connecting portions from one another in the vertical direction.
However, since the connecting portions of the band-shaped core sheets are bent at the time of producing the laminated core, the bent connecting portions are bulged in the thickness direction compared to those yet to be bent. Thus, in the art disclosed in Japanese Unexamined Patent Application Publication No. 1-264548, there is a possibility that the bent connecting portions come into contact with the band-shaped core sheets overlaid in the vertical direction to thereby generate gaps therebetween. Compared to a core laminated without gaps, a core with gaps may require an extra pressure treatment to eliminate the gaps, or cause efficiency reduction or vibration of a motor, which results in reduction in product quality.
The present invention has been made in view of the circumstances, and thus an object of the present invention is to provide a laminated rotor core having favorable shape accuracy and product quality, and a method for manufacturing the laminated rotor core with high productivity by winding band-shaped core sheets.